1. Field of Invention
The present invention relates to a coupled torsion beam axle type suspension system, and more particularly, to a coupled torsion beam axle type suspension system for simultaneously improving impact and roll characteristics of an outer rear wheel with respect to thrust and drag forces as well as controlling movement (e.g., toe) characteristics thereof with respect to a side force, when a vehicle turns.
2. Description of Related Art
Generally, despite a limitation in design performance factors such as ride comfort, driving stability, etc., a coupled torsion beam axle type suspension system (hereinafter referred to as a CTBA) has been primarily applied to rear wheel suspension systems for compact and mid-size cars, compared with independent-type suspension systems, because they have advantages of light weight and low production cost due to their simpler components.
FIG. 1 is a perspective view of a CTBA according to one example of the related art. Referring to FIG. 1, a CTBA according to one example of the related art is provided with a torsion beam 1 in a width direction of a vehicle, trailing arms 5 respectively coupled to opposite ends of the torsion beam 1, and carriers 3 for mounting wheel tires at the trailing arms 5.
A spring seat 9 for mounting a spring 7 thereon and a shock absorber pin 13 for coupling with a shock absorber 11 are provided at a rear inner portion of the trailing arm 5. In addition, a vehicle body-engaging unit 15 is provided at a front end portion of the trailing arm 5 to be coupled to a vehicle body. Each vehicle body-engaging unit 15 includes a trailing arm bush 21 that is coupled to the front end portion of the trailing arm 5, and a mounting bracket 23 that is coupled to the trailing arm bush 21 through a bolt 25.
According to the CTBA having the aforementioned configuration, wheels are deformed due to twisting deformation characteristics of the torsion beam 1, and in addition to that, a position of the trailing arm 5 and a configuration of the vehicle body-engaging unit 15 cause deformation of the wheels.
The vehicle should maintain an under-steering tendency in consideration of driving stability when it turns, and for this purpose, it is ideal that a rear outer wheel of a turning vehicle (hereinafter referred to as a rear outer wheel) should be induced to toe-in and a rear inner wheel of the turning vehicle (hereinafter referred to as a rear inner wheel) should be induced to toe-out.
However, the conventional CTBA has following problems in its movement.
FIG. 2 is a top plan view illustrating movement characteristics of the coupled torsion beam axle type suspension system, applied with a side force, according to one example of the related art. As shown in FIG. 2, though the CTBA according to one example of the related art is not freely moveable in terms of mechanics when applied with a side force F1 , the entire CTBA rotates by the deformation of the trailing arm bush 21 and generates a toe angle at the rear outer wheel W1. That is, when the vehicle turns, the bumped rear outer wheel W1 is applied with the side force F1 and thus is likely to be induced to toe-out, while the rebounded rear inner wheel W2 is applied with the side force F1 and thus is likely to maintain the previous toe angle or to be induced to toe-in, such that the vehicle is over-steered in general and thus causes deterioration of turning stability.
As a mechanical instantaneous rotational center point SP of the CTBA with respect to the vehicle body (i.e., an intersection of lines that extend in engaging directions of the trailing arm bushes 21 engaged with the vehicle body) is positioned in front of the wheel centers WC, the rear outer wheel W1 has a tendency to toe-out due to the side force F1 while the rear inner wheel W2 has a tendency to toe-in due to the side force F1.
Recently, in order to solve such turning stability problems of the conventional CTBA, suspension systems are being developed to improve a structure of the vehicle body and the vehicle body-engaging unit of the trailing arm 5 such that the instantaneous rotational center point SP of the CTBA with respect to the vehicle body is positioned behind the wheel centers WC.
FIG. 3 is a top plan view of a coupled torsion beam axle type suspension system according to another example of the related art. Referring to FIG. 3 the improved CTBA according to the other example is provided with a link bracket 31 as a vehicle body-engaging unit 15 between a vehicle body and a trailing arm bush 21, such that an instantaneous rotational center point SP with respect to the vehicle body is positioned behind wheel centers WC.
That is, a rear end portion of the link bracket 31 is parallelly engaged with the trailing arm bush 21 in a width direction of the vehicle, and a front end portion thereof is provided with a vehicle body-mounter 33 that is freely rotatable with respect to the vehicle body in a rotating direction, thereby being engaged with one lower portion of the vehicle body.
In this case, the vehicle body-mounter 33 is coupled to the trailing arm bush 21 through the link bracket 31 and is engaged with the vehicle body in the height direction of the vehicle, such that it is engaged with the vehicle body at a front end portion of the link bracket 31 in the width direction of the vehicle.
Thus, the instantaneous rotational center point SP of the CTBA with respect to the vehicle body is formed at an intersection of the extending lines that connect centers S1 of the mounter 33 with centers S2 of the trailing arm bushes 21, and is positioned behind the wheel centers WC.
As such, in the CTBA according to the current example, the instantaneous rotational center point SP with respect to the vehicle body is positioned behind the wheel centers WC, such that it has following movement characteristics with respect to the side force F1 and the thrust and drag forces.
FIGS. 4 C1, C2, and C3 are top plan views illustrating movement characteristics of the coupled torsion beam axle type suspension system, applied with the side force and the thrust and drag forces, according to another example of the related art.
In FIG. 4 C1, when rear wheels are applied with the side force F1 , the bumped rear outer wheel is induced to toe-in while the rebounded rear outer turning wheel W2 maintains a set toe-in angle or is induced to toe-out, such that the vehicle is generally under-steered to secure the turning stability.
Meanwhile, the CTBA is induced to rotate based on the instantaneous rotational center point SP when the rear wheels are applied with the thrust and drag forces F2 as well as the side force F1 . That is, in FIG. 4 C2, in the CTBA according to another example, in a double impact environment in which the rear wheels are simultaneously applied with the thrust and drag forces, such as when the vehicle brakes or passes over a speed bump, rotation of the CTBA is offset by symmetrical rotation of the rear wheels, thereby guaranteeing the driving stability.
However, in FIG. 4 C3, in a single impact environment in which one of the rear wheels is asymmetrically applied with the thrust and drag forces F2 , the corresponding rear wheel is induced to toe-out which makes the movement characteristics of the CTBA unstable in general, thereby deteriorating the driving stability as in the previous example according to the related art.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.